Method and medium for the detecting/identifying microorganisms with esterase and/or r osidase and/or peptidase and/or sulfatase and/or phosphatase activity

ABSTRACT

The invention relates to a medium for biological analysis by biochemical means involving chromogenic or fluorogenic substrates that react with enzymes (esterases and/or osidases and/or peptidases and/or sulfatases and/or phosphatases) specific for the target strains. The object of the invention is to improve the sensitivity, initial translucence, stability and ease of use of such identification/detection media. This object is achieved by the medium according to the invention, which is in a stable, ready-to-use liquid or gel form and contains at least one emulsifying stabilizer of the fatty acid sorbitan ester/fatty acid type and at least one solvent (dimethyl sulfoxide). This medium is obtained by mixing a stock solution of esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrates in the solvent, and the emulsifying stabilizer, with some of the constituents of the culture medium. The invention further relates to the preparation of such a medium and to the use of a fatty acid sorbitan ester/fatty acids as an emulsifying stabilizer in a medium for the detection/identification of microorganisms, especially bacteria or yeasts, with esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities.

The field of the invention is that of microbiological analysis by biochemical means and in particular the detection and identification of bacterial strains by the inoculation of reaction media, particularly nutrient media. The latter comprise chromogenic or fluorogenic substrates that are capable of reacting with enzymes specific for the target strains to produce a coloration or a fluorescence for each colony in question.

Of more particular interest within the framework of the present invention is the detection/identification of pathogenic or quality-indicating microorganisms, whether in a medical or industrial environment, and more particularly microorganisms with an enzymatic activity of the esterase, osidase, peptidase, sulfatase or phosphatase type, for example bacteria or yeasts of the genera Salmonella, Pseudomonas, Listeria, Staphylococcus, Enterococcus and Candida and more particularly those of the species Escherichia coli, Listeria monocytogenes, Staphylococcus aureus and Candida albicans.

The presence of strains of Escherichia coli is often demonstrated by revealing an enzymatic activity of the osidase type, such as β-glucuronidase or β-galactosidase activity.

Likewise, the genus Listeria is detected by revealing the presence of β-glucosidase activity.

An aminopeptidase activity can also be utilized to reveal a group, a genus or a species of microorganisms. Alanine aminopeptidase activity, for example, makes it possible to differentiate between Gram-negative bacteria and Gram-positive bacteria.

The genus Salmonella, which is responsible for a variety of infections (typhoid fever, food poisoning) in humans, possesses non-specific esterases capable of hydrolyzing chromogenic, for example indigogenic, synthetic substrates.

The detection/identification of salmonellae, and more generally of bacteria with esterase activity, is conventionally carried out on gelose or liquid isolating media that allow the detection/identification of suspect colonies of bacteria with esterase activity, especially salmonellae. The inoculation of such media is effected by immersing said medium in the sample analyzed or by bringing the sample into contact with the medium.

In their enzymatic genotype, bacteria with esterase, osidase, peptidase, sulfatase or phosphatase activities possess esterases, osidases, peptidases, sulfatases or phosphatases which cleave the target linkages of the substrates present in the medium and thus release the activated chromophoric or fluorophoric part of said substrates. This results in a coloration or a fluorescence that reveals hydrolysis and hence the presence of target bacteria or colonies of target bacteria.

To be able to perform routine tests on a large scale, it is necessary for the detection/identification media to be stable and to enable the corresponding detection/identification methods to be simplified as far as possible by limiting the manipulations. Also, it is important for the methods to offer a high sensitivity (high intensity of coloration) and a first order specificity. Another fundamental parameter of these types of media and methods for the detection/identification of bacteria exhibiting the above-mentioned enzymatic activities is the rate at which the suspect colonies are revealed.

Now, it is known that enzyme substrates such as esterases, osidases, peptidases, sulfatases or phosphatases present problems of compatibility with culture media for microorganisms, particularly bacteria, possessing these activities. Furthermore, such substrates are not stable over time, meaning that the sensitivity towards the enzymatic activity in question decreases with storage time.

In this context the scientific article entitled “Synthèse de substrats indigogéniques. Mise en évidence de l'activité estérasique des salmonelles” (“Synthesis of indigogenic substrates. Demonstration of the esterase activity of salmonellae”): A. Agban et al., Eur. J. Med. Chem. (1990) 25, 697-699, discloses gelose culture media comprising indigogenic substrates, namely 5-bromoindoxyl pelargonate (C9) in particular, and a bile salt, namely sodium deoxycholate. Such culture media suffer from the same disadvantages as those referred to below with reference to patent document FR 2 697 028.

Patent FR 2 697 028 discloses a culture medium for revealing the presence of salmonellae which comprises a chromogenic esterase substrate consisting of an ester of caprylic acid with an indole radical (5-bromo-4-chloro-3-indolyl caprylate), together with a detergent selected from bile salts (sodium deoxycholate). This chromogen and this bile salt are contained in a nutrient medium that allows salmonellae to grow. According to the teaching of FR 2 697 028, the bile salt is added directly to the selective medium already containing the esterase substrate.

Another disadvantage associated with the use of bile salts derives from the fact that they are starting materials of animal origin, which underlies a certain variability in quality.

In addition, the results in terms of biological activity are capable of improvement.

This culture medium does not offer all the desirable guarantees in terms of stability of the esterase substrate. Moreover, the latter proves to be incompletely miscible with the culture medium, which obviously detracts from the quality of the results obtained from the point of view of sensitivity, rapidity and stability.

It must also be noted that the culture medium according to FR 2 697 028 is in the form of a powder. This means that the user first has to carry out an operation to reconstitute the liquid or gelled medium. This constraint is a consequence of the lack of stability of the esterase substrates used. In addition, the gelose medium prepared according to the teaching of FR 2 697 028 is not translucent, which is likely to compromise the reading of the colorations associated with any colonies of target bacteria.

PCT patent application WO-92/17607 relates to a detection medium for salmonellae which contains TERGITOL-4® (7-ethyl-2-methyl-4-undecanoate hydrogensulfate or its sodium salt). This additive is supposed to improve the selectivity of the detection medium towards target salmonellae. The concentration of TERGITOL-4® can vary from 2 to 30 ml/l in the culture medium based on agar gelose/xylose/lysine. According to said document, the detection of salmonellae is based solely on a principle of selective growth by competition.

PCT patent application WO-99/41409 relates to chromogenic esterase substrates for the detection of salmonellae.

Said document proposes the use of a chromogenic compound which reacts with an esterase/lipase specific for the genus Salmonella and having an affinity for C8 fatty acid esters. The chromogenic compound in question comprises an anion and a cation of the formula [4-[2-(4-octanoyloxy-3,5-dimethoxyphenyl)vinyl]-quinolinium-1-(propan-3-yl)carboxylate]⁺.⁻[bromide or chloride]. More precisely, the substrates used are C8 esters, for example, of the carboxylate cation.

Also, the method according to WO-99/41409 describes the use of a sorbitan fatty acid ester (particularly the monolauric acid ester TWEEN® 20). These products are employed as detergents at a rate of 2 g per liter of medium.

In addition, the specific substrate according to the teaching of said PCT patent application can be introduced into the nutrient culture medium as a mixture with methanol, ethanol or N,N-dimethylformamide (DMF). The detergent, if used, is introduced separately rather than together with the substrate and the solvent.

Whatever the case may be, the means disclosed in WO-99/41409 are not presented as providing an improvement in the stability of the enzyme substrates contained in the detection medium.

Various documents also disclose culture media containing several substrates for the detection of a single enzymatic activity, as well as culture media containing several substrates for the detection of different enzymatic activities.

Patent document WO-95/04157, for example, describes culture media containing different chromogenic osidase substrates such as 5-bromo-4-chloro-3-indoxylgalactoside, 5-bromo-4-chloro-3-indoxylglucuronide, 5-bromo-4-chloro-3-indoxylglucoside or 6-chloro-3-indoxylgalactoside. Such media are used to differentiate especially between bacteria of the species Escherichia coli and other coliform bacteria.

Said document further describes a medium containing chromogenic substrates specific for different enzymes such as osidases and phosphatases. Examples of these substrates are 5-bromo-4-chloro-3-indoxyl N-acetyl-glucosaminide and 5-bromo-6-chloro-3-indoxyl phosphate. Such a medium makes it possible in particular to differentiate between Candida albicans and other yeasts of the genus Candida.

Patent document WO-00/53799 describes a chromogenic medium for the detection of Staphylococcus aureus bacteria. This medium contains two chromogenic substrates in combination, especially 5-bromo-4-chloro-3-indoxyl-glucoside and 5-bromo-6-chloro-3-indoxyl phosphate. The principal value of such a medium is avoiding false positives or false negatives and differentiating between S. aureus and other species or other genera such as Streptococcus.

However, patent documents WO-95/04157 and WO-00/53799 give no indication that the media described were developed in order to improve the stability of the enzyme substrates they contain.

Fatty acid sorbitan esters (FASE) are known surfactants that are widely used especially in food and pharmaceutical preparations. By way of illustration, there may be mentioned the article by DICKINSON et al. in “J. Colloid Interface Sci. Apr. 15, 1999; 212 (2): 466-473”, which relates to the stabilization of emulsions containing sodium caseinate and a polyethoxylated sorbitan monolaurate containing 20 units of ethylene oxide (TWEEN 20). The emulsions in question are oil-in-water emulsions (30% by volume of n-tetradecane at pH 6.8). This technical field is relatively remote from that of the detection of bacteria with specific enzymatic activity by means of a color reaction on a selective culture medium.

The article by GRAM et al. in “Clin. Chem. October 1985; 31 (10): 1683-8” concerns the use of polyethoxylated sorbitan monooleate (TWEEN 80) in an antithrombin-III assay medium, said medium also containing polyethylene glycol, a solution of thrombin and synthetic chromogenic peptide substrates. The additives used are presented as allowing an increase in the concentration of active thrombin so as to guarantee that the analysis performs well. Once again, one is forced to observe that technical concerns of this kind are very different from those peculiar to a medium for the detection of bacteria with specific enzymatic activity using selective culture media containing chromogenic substrates.

In such a technical environment, one of the essential objectives of the present invention is to provide a medium for the detection/identification of bacteria with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities which is made up in such a way as to optimize the sensitivity of the analysis, i.e. maximize the intensity of the coloration or fluorescence revealing the presence of target bacteria.

Another essential objective of the present invention is to provide a medium for the detection/identification of microorganisms, especially bacteria or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities which is perfectly translucent before inoculation with the sample to be analyzed.

Another essential objective of the invention is to provide a medium for the detection/identification of microorganisms, especially bacteria or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities which contains at least one chromogenic or fluorogenic enzyme substrate selected from esterase substrates and/or osidase substrates and/or peptidase substrates and/or sulfatase substrates and/or phosphatase substrates and is stable on storage (intensity of the revealed coloration or fluorescence maintained at a maximum level for at least several weeks).

Another essential objective of the invention is to provide a medium for the detection/identification of microorganisms, especially bacteria or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities which is not in the form of a dry powder that has to be regenerated with a liquid in order to reconstitute a liquid or gelled medium, but which exists directly in ready-to-use forms.

Another essential objective of the invention is to provide a medium for the detection/identification of microorganisms, especially bacteria or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities which is economic, especially due to the fact that it comprises reduced amounts of one or more chromogenic or fluorogenic enzyme substrates, which are characteristically expensive.

Another essential objective of the invention is to provide a method of obtaining the above-mentioned detection/identification medium which is simple to carry out and economic.

Another essential objective of the present invention is to provide a method for the detection/identification of strains with an enzymatic activity selected from esterase, osidase and/or peptidase and/or sulfatase and/or phosphatase activities which is easy to carry out (routine tests), economic (amount of reagent, handling, label, speed, etc.), reliable, sensitive, specific and reproducible.

Another essential objective of the present invention is to propose the use of a novel stabilizing additive in media for the detection/identification of microorganisms, especially bacteria or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities, said activity being revealed as a result of a hydrolysis reaction which releases a dye or a fluorescent product.

These and other objectives are achieved by the present invention, which relates first and foremost to a medium for the detection/identification of microorganisms, especially bacteria and/or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities that is of the type comprising especially a reaction medium, particularly a culture medium, and at least one chromogenic or fluorogenic esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrate, with the exclusion of substrates comprising a 4-[2-(4-octanoyloxy-3,5-dimethoxyphenyl)-vinyl]quinolinium-1-(propan-3-ylcarboxylic acid) cation and an anion, this detection/identification being based essentially on revealing the presence of the esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities, . . . said medium:

-   -   is in a stable, ready-to-use liquid or gel form; and     -   contains:         -   at least one fatty acid sorbitan ester (FASE) or at least             one fatty acid (FA) or an FASE/FA mixture (comprising at             least one fatty acid sorbitan ester and at least one fatty             acid) as an emulsifying stabilizer, and         -   optionally at least one solvent (S).

A medium for the detection/identification of microorganisms, especially bacteria and/or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities, according to the invention, can be obtained from the media presented in patent documents WO-95/04157 and WO-00/53799 described above.

The medium according to the invention has the advantage that it is ready to use and is in a liquid or semiliquid (gel) form without presenting a problem in terms of stability. In fact, the esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrates present in this medium, even though they are known for their tendency to degrade relatively rapidly, are stabilized through the presence of the FASE, FA or FASE/FA stabilizing-emulsifying additive.

This additive, optionally associated with the solvent S, brings a further advantage, namely allowing an excellent dissolution of the esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrates, which are traditionally reluctant to dissolve. This makes it possible to obtain detection/ identification media that are translucent before inoculation, thereby making it easier to read the coloration or fluorescence results.

This FASE, FA or FASE/FA additive is relatively inexpensive and makes it possible to simply the procedure and to reduce the amount of substrates used (stabilization), resulting in a definite saving in economic terms.

Finally, the means according to the invention give rise to an improvement in the biological activity of the afore-mentioned substrates, resulting in a more intense coloration of the target colonies and a better specificity.

It is to the inventors' credit to have selected this particular class of emulsifying stabilizers, particularly FASE, which surprisingly and unexpectedly afford properties of stability, translucence, biological activity, sensitivity, reliability and specificity that are altogether apposite in the microbiological analysis by biochemical means according to the invention.

According to one noteworthy characteristic of the invention, the detection/identification medium to which it relates is obtained by mixing at least one stock solution of the substrate in the solvent S with FASE, FA or an FASE/FA mixture, and with at least some of the constituents of the culture medium.

In fact, it appears to be important according to the invention to solubilize the esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrate in the solvent S in the presence of one or more FASE or FA or an FASE/FA mixture as defined above. This mixture of FASE, FA or FASE/FA substrate and solvent S is then incorporated into at least part of the culture medium, which is preferably in a supercooled gelled form. It has been found that this operating characteristic makes it possible to optimize the advantageous results produced by the means according to the invention.

Preferably, the FASE is selected from the group comprising:

-   -   polyethoxylated sorbitan monolaurate containing 20 units of         ethylene oxide (EO)—TWEEN® 20 -;     -   polyethoxylated sorbitan monopalmitate (20 EO)—TWEEN® 40-;     -   polyethoxylated sorbitan monostearate (20 EO)—TWEEN® 60-;     -   polyethoxylated sorbitan tristearate (20 EO)—TWEEN® 65-;     -   polyethoxylated sorbitan monooleate (20 EO)—TWEEN® 80-;     -   polyethoxylated sorbitan sesquioleate (20 EO)—TWEEN® 83-;     -   polyethoxylated sorbitan trioleate (20 EO)—TWEEN® 85-; and     -   mixtures thereof,         and the FA is selected from the group comprising C4-C20         saturated or unsaturated fatty acids, preferably C6-C11         saturated or unsaturated fatty acids and particularly preferably         C8-C9 fatty acids, and mixtures thereof.

The products particularly selected according to the invention are sorbitan esters that are widely used in the food and cosmetic industries as non-ionic emulsifiers, but hitherto they have never been employed in microbiological detection/identification media as stabilizers for esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrates.

The Hydrophilic-Lipophilic Balances (HLB) of the above-mentioned FASE are respectively 8.6, 6.7, 4.7, 2.1, 4.3, 3.7 and 1.8.

In one advantageous variant of the invention, the emulsifying stabilizer(s) described above, in particular the FASE(s), can be associated with at least one synergistic co-agent, preferably at least one anionic surfactant and particularly preferably 7-ethyl-2-methyl-4-undecyl hydrogensulfate or its salts, more particularly its sodium salts (TERGITOL-4®).

The use of such a synergistic co-agent makes it easier to reveal the presence of the enzymatic activity in the target bacteria. Said co-agent is an excellent complement to the emulsifying stabilizer(s) and particularly the FASE. It makes it possible to improve the selectivity and the detection of the esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities in the target microorganisms without detracting from the expression of other enzymatic activities which might possibly be used to reveal the presence of the target microorganisms in question. Without wishing to be bound by theory, it is assumed that the synergistic co-agent TERGITOL-4® has an action which favors the penetration of the chromogenic or fluorogenic esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrates or the excretion of the enzymes across the membranes of the cells of the target microorganisms, thereby optimizing the accessibility of these substrates in respect of the enzymes whose activity is sought. This makes it possible to reduce the amount of substrates used and derive a definite economic advantage therefrom.

Even more preferably, the combination of TWEEN® and TERGITOL-4® seems to be totally effective in the detection/identification medium according to the invention.

The chromogenic or fluorogenic substrate, consisting of a target part for the enzyme and a chromophoric or fluorophoric part, is advantageously chosen from substrates whose target part is selected from the group comprising the following in particular:

-   -   glycosides consisting of mono-, di- and/or polysaccharide units         linked in the α- or β-position to the hydroxyl group of the         chromophoric or fluorophoric part;     -   α-amino acids or peptides;     -   organic acids such as —O—CO(CH₂)n—CH₃, where n is between 0 and         20; and     -   a sulfate, a phosphate, a pyrosulfate, a pyrophosphate and a         phosphodiester,         and whose chromophoric or fluorophoric part is selected from the         group comprising the following in particular:     -   quinones/anthraquinones and derivatives, especially         dihydroxyanthraquinone (alizarin);     -   amino- and hydroxycoumarins and derivatives;     -   fluoresceins and derivatives; and     -   indoxyls and derivatives.

Examples of esterase substrates which may be mentioned are chromogenic ester substrates derived from indole, especially 5-bromo-3-indolyl nonanoate, 6-chloro-3-indolyl nonanoate or 5-bromo-3-indolyl decanoate.

2-Alizarin octanoate may be mentioned as an example of a chromogenic esterase substrate derived from anthraquinone.

Examples of osidase substrates which may be mentioned are chromogenic osidase substrates derived from indole, especially 6-chloro-3-indolyl-β-galactoside, 5-bromo-4-chloro-3-indolyl-β-N-acetylglucosaminide or 5-bromo-6-chloro-(α-glucoside.

2-Alizarin-β-glucuronide may be mentioned as an example of a chromogenic osidase substrate derived from anthraquinone.

Fluorogenic osidase substrates which may be mentioned are substrates derived from hydroxycoumarin, especially 4-methylumbelliferone-β-glucoside.

Substrates derived from indole may be mentioned as chromogenic peptidase substrates.

Fluorogenic peptidase substrates are especially substrates derived from hydroxycoumarin, such as alanylaminomethylcoumarin.

Sulfatase substrates which may be mentioned are chromogenic substrates derived from indole, particularly 5-bromo-4-chloro-3-indolyl sulfate. 4-Methyl-umbelliferone sulfate is an example of a fluorogenic sulfatase substrate.

In an equivalent manner, phosphatase substrates which may be mentioned are chromogenic substrates derived from indole, such as 5-bromo-4-chloro-3-indolyl phosphate. 4-Methylumbelliferone phosphate is an example of a fluorogenic phosphatase substrate.

The solvent S is an auxiliary for solubilizing the enzyme substrate of interest, particularly a chromogenic enzyme substrate. It also complements the action of the FASE, FA or FASE/FA emulsifying stabilizer. It is therefore preferably a constituent of the medium according to the invention.

According to an advantageous provision of the invention, the solvent S is selected from the group comprising:

-   -   alcohols, preferably methanol, ethanol and methoxyethanol;     -   amides, preferably dimethylformamide (DMF);     -   sulfur-containing solvents, preferably dimethyl sulfoxide         (DMSO);     -   aqueous solvents, preferably water and buffered water; and     -   mixtures thereof.

In practice, the solvents preferably used are methanol, DMF and DMSO.

It has been found altogether advantageous according to the invention for the proportion by weight of fatty acid sorbitan ester(s) (FASE) to solvent (S) to be between 20:80 and 80:20, preferably between 30:70 and 70:30 and particularly preferably 40:60 or 60:40.

Still from the quantitative point of view, it is preferable for the concentration of (FASE) in the medium to be defined as follows (in % by weight): 0.1 ≦ [FASE] ≦ 10, preferably 0.5 ≦ [FASE] ≦ 5, and particularly preferably 1.5 ≦ [FASE] ≦ 3.5.

The amounts of chromogenic or fluorogenic substrate used are such that its concentration in the medium is defined as follows (in mg/l):  1 ≦ [substrate] ≦ 2000, preferably  5 ≦ [substrate] ≦ 1500, and particularly preferably 25 ≦ [substrate] ≦ 1000.

The amounts of substrate used in the solution of FASE and solvents S are such that its concentration in the medium is defined as follows (in g/l): 0.5 ≦ [substrate in stock solution] ≦ 2000, preferably   1 ≦ [substrate in stock solution] ≦ 1000, and particularly   2 ≦ [substrate in stock solution] ≦ 200. preferably

As regards the culture medium present in the detection/identification medium, it can be specified that it is selected from the group comprising:

-   -   selective media of the type comprising MacConkey, Columbia ANC,         PALCAM and Sabouraud gentamycin-chloramphenicol media,         preferably MacConkey medium; and     -   non-selective media of the type comprising Columbia ± blood,         trypcase soya, nutrient gelose and Sabouraud media, preferably         Columbia medium.

In practice, those skilled in the art will choose the culture medium according to the target bacteria and according to perfectly known criteria with which they are familiar.

Without implying a limitation, it is found that the medium according to the invention is particularly suitable for the detection/identification of microorganisms of medical or industrial interest, especially those of the genus Salmonella, Pseudomonas, Listeria, Staphylococcus, Enterococcus or Candida.

In the case of the detection of bacteria of the genus Salmonella, MacConkey medium, for example, will be chosen as the culture medium.

Furthermore, the medium according to the invention can optionally contain other additives such as one or more other enzyme substrates, for example chromogenic or fluorogenic enzyme substrates, peptones, one or more growth factors, carbohydrates, one or more selective agents, buffers and one or more gelling agents.

The medium according to the invention is in the form of a liquid or gel that is ready to use, i.e. ready for inoculation in a tube or flask or on Petri dishes.

The medium according to the invention can be stored in its containers for several weeks at 4° C. in liquid or gel form.

According to another of its features, the present invention further relates to a method of obtaining the medium as defined above, characterized in that it consists essentially in:

-   -   preparing at least one stock solution of the chromogenic or         fluorogenic esterase and/or osidase and/or peptidase and/or         sulfatase and/or phosphatase substrate in the solvent S and of         at least one FASE, FA or FASE/FA mixture,     -   adding this solution and any other additives to the culture         medium, and     -   homogenizing the whole.

The stock solution is prepared separately by successively incorporating the substrate, the solvent S and the FASE, FA or FASE/FA mixture, optionally containing co-additives. The products and the amounts used are as defined above.

After homogenization, the stock solution is added to the supercooled gelled culture medium which has been regenerated in water beforehand. The medium can also be a non-gelled liquid medium, for example a nutrient broth.

Mixing of the culture medium and the stock solution gives the liquid or gelled detection medium ready for inoculation.

According to yet another of its features, the invention further relates to a method for the detection/identification of strains with esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activity which consists in:

-   -   inoculating the detection/identification medium as defined         above, either as a product per se or as a product obtained by         the method also described above, with the sample containing the         target bacteria to be analyzed;     -   incubating the inoculated medium under appropriate conditions         known to those skilled in the art; and     -   reading/interpreting the colorations or fluorescences of the         colonies which have developed after incubation, for example in         an oven at 37° C., these colorations revealing hydrolysis of the         chromogenic or fluorogenic esterase and/or osidase and/or         peptidase and/or sulfatase and/or phosphatase substrate by the         target bacteria.

Finally, the invention further relates to the use of fatty acid sorbitan ester(s) (FASE), fatty acids (FA) or an FASE/FA mixture as an emulsifying stabilizer for a medium (liquid or gel) for the detection/identification of microorganisms, especially bacteria or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities, this medium comprising especially a reaction medium and at least one chromogenic or fluorogenic esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrate, with the exclusion of substrates comprising a 4-[2-(4-octanoyloxy-3,5-dimethoxyphenyl)vinyl]quinolinium-1-(propan-3-yl)carboxylate and an anion, optionally in association with at least one solvent S for the chromogenic or fluorogenic esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrate present in the medium.

The Examples which follow will provide a clearer understanding of the invention and make it possible to assess all its advantages as well as its diverse embodiments and modes of implementation.

EXAMPLES Example 1 Testing the Solubility of the Indoxyl-Based Esterase Substrate 5-bromo-3-indolyl Nonanoate (Chromogenic Esterase Substrate) in a Gelled Medium

Different stock solutions of substrate are prepared in methanol in the presence of no. 3 bile salts (bioMérieux). Different volumes of these solutions are then added to a supercooled gelled medium, namely MacConkey medium (regenerated in water at a concentration of 50 g/l).

The protocol and the appearance of the media are collated in Table 1 below. TABLE 1 Medium 1 2 3 4 5 Substrate concentration 100 g/l 50 g/l 25 g/l 12.5 g/l 6.25 g/l of the stock solution Final substrate 500 mg/l concentration of the medium Bile salt concentration 5 g/l 2.5 g/l of the stock solution Total bile salt 7.5 g/l 4 g/l concentration of the medium Methanol concentration 0.5% 1% 2% 4% 8% of the medium Observation of the precipitate precipitate slight milky milky medium poured into in the form in the form precipitate: medium medium dishes of coarse of smaller milky grains grains than medium in medium 1

The most optically homogeneous media are 3, 4 and 5, being the media in which the methanol concentration is greatest. However, these media have a “milky” appearance, so it would seem that the esterase substrate is in the form of an emulsion.

Example 2 Improving the Solubilization of the Esterase Substrate by Adding Tween® 20 (FASE)

Two different stock solutions of substrate are prepared in methanol as the solvent S, one in the presence of no. 3 bile salts and the other in the presence of no. 3 bile salts and Tween® 20 [polyethoxylated sorbitan monolaurate containing 20 units of ethylene oxide (EO)]. A volume corresponding to a final concentration of 500 mg/l of substrate is then added to a supercooled gelled culture medium, namely MacConkey medium. The protocol and the appearance of the media are collated in Table 2 below. TABLE 2 Medium 1 2 Substrate concentration of 100 g/l 40 g/l the stock solution Final substrate concentration 500 mg/l 500 mg/l of the medium Bile salt concentration of 5 g/l 5 g/l the stock solution Total bile salt concentration 6.5 g/l 6.5 g/l of the medium Concentration of Tween ® 0%  60% 20 added to the stock solution of substrate Concentration of Tween ® 0% 2.5% 20 added to the medium Observation of the medium milky translucent poured into dishes medium medium

Medium 2 has a better optical homogeneity than medium 1. The esterase substrate is either completely dissolved or in the form of an emulsion whose micellar particles are no longer visible to the eye.

Example 3 Biological Testing of the Two Media Described in the Previous Example

Microorganisms originating from the Applicant's collection were inoculated onto each of the two media described above from a 0.5 McFarland suspension by isolation in three quadrants. The dishes were incubated at 37° C. for 48 hours. The colonies formed were examined visually after 24 and 48 hours of incubation. The coloration of these colonies and the intensity of this coloration were noted. The results are shown in Table 3 below. TABLE 3 incubation medium 1 medium 2 Strain time color intensity color intensity Salmonella 24 h gray 1.5 gray 3 typhimurium 10 48 h gray 1.5 gray 3.5 Salmonella 24 h gray 1 gray 3 paratyphi A 152 48 h gray 1.5 gray 3.5 Proteus 24 h — — — — vulgaris 15 48 h — — — — Serratia 24 h gray 1.5 gray 3 marcescens 13 48 h gray 1 gray 4 intensity of coloration: arbitrary scale; —: absence of coloration or intensity

The medium containing Tween® 20 therefore makes it possible to obtain more intense colorations for the strains of microorganisms exhibiting an esterase activity. The substrate is therefore more widely used either because it dissolves better or because it is more readily available. In view of the difference in intensity between the two media, it seems to be possible, in the presence of Tween® 20, to reduce the concentration of substrate used and hence to lower the cost incurred by the use of this type of substrate.

Example 4 Testing this Mode of Dissolution for Another Indoxyl Derivative (Chromogenic Esterase Substrate) on Gram-positive and Gram-negative Bacterial Species and Yeasts

A 40 g/l stock solution of 5-bromo-4-chloro-3-indolyl octanoate (chromogenic esterase substrate) was prepared in a mixture of methanol (40%) and Tween® 20 (60%). A volume corresponding to a final concentration of 500 mg/l of substrate was then added to a supercooled gelled medium, namely a medium of the Columbia type. This medium was poured into Petri dishes.

Microorganisms originating from the Applicant's collection were inoculated from a 0.5 McFarland suspension by isolation in three quadrants. The dishes were then incubated at 37° C. for 48 hours. The colonies formed were examined visually after 24 and 48 hours of incubation. The coloration of these colonies and the intensity of this coloration were noted. The results are shown in Table 4 below. TABLE 4 incubation medium 1 Strain time color intensity Listeria 24 h turquoise 2.5 monocytogenes 023 48 h turquoise 2.5 Listeria 24 h — — innocua 029 48 h turquoise 0.5 Staphylococcus 24 h turquoise 2.5 aureus 276 48 h turquoise 3 Candida 24 h turquoise 0.5 albicans 033 48 h turquoise 3 Staphylococcus 24 h turquoise 2 epidermidis 009 48 h turquoise 2 Salmonella spp. 24 h turquoise 2 017 48 h turquoise 3 Proteus 24 h — — vulgaris 015 48 h — — intensity of coloration: arbitrary scale; —: absence of coloration or intensity

In the presence of Tween 20, it is therefore possible to reveal the expression of an esterase activity in all microorganisms that exhibit it, independently of the group to which they belong. Furthermore, this mode of use is independent of the indoxyl derivative (chromogenic esterase substrate) studied.

Example 5 Replacing Methanol with Other Solvents in the Presence of Tween 20 and in the Presence of Bile Salts

The methanol used in the previous Examples was replaced with two other solvents, namely dimethyl sulfoxide (DMSO) and dimethylformamide (DMF). The three solvents were tested in the presence of Tween 20 and in the presence or absence of bile salts at a final concentration of 6.5 g/l in the medium. Table 5 below shows the composition of the six media tested. TABLE 5 Medium 1 2 3 4 5 6 Solvent S of the methanol DMSO DMF methanol DMSO DMF stock solution (SS) % of solvent S in 40% the SS % of Tween ® 20 60% added to the SS of substrate Bile salt 6.5 g/l 0 g/l concentration of the medium Final substrate 500 mg/l concentration of the medium

The activity of the substrate was verified in the same way as in the previous Example, i.e. in the presence of microorganisms inoculated onto a MacConkey gelose medium containing the esterase substrate dissolved in one of the solvents mentioned above. The results are shown in Table 6 below. TABLE 6 Medium 1 2 3 4 5 6 Strain IT C I C I C I C I C I C I Salmonella 24 gray 2 gray 2 gray 2 gray 2 gray 2 gray 2 typhimurium 10 48 gray 2.5 gray 2.5 gray 2.5 gray 2.5 gray 2.5 gray 2.5 Salmonella 24 gray 2 gray 2.5 gray 2 gray 2 gray 2.5 gray 2 arizonae 15 48 gray 2.5 gray 3 gray 2.5 gray 2.5 gray 3 gray 2.5 Pseudomonas 24 gray 2 gray 2 gray 1 gray 2 gray 2 gray 1 aeruginosa 15 48 gray 2.5 gray 4 gray 3.5 gray 3 gray 4 gray 4 Proteus 24 — — — — — — — — — — — — vulgaris 15 48 — — — — — — — — — — — — Serratia 24 gray 2.5 gray 2 gray 2 gray 2.5 gray 2 gray 2 marcescens 38 48 gray 2.5 gray 2 gray 2 gray 2.5 gray 2 gray 2 I: intensity of coloration (arbitrary scale); C: color; IT: incubation time in hours; —: colorless

It is therefore possible to use different solvents to dissolve the esterase substrate when Tween 20 is present. Furthermore, the addition of bile salts makes no difference, whether in terms of solubility or in terms of biological results, irrespective of the solvent tested. It is concluded that the simplest mode of dissolution is to mix a solvent and Tween® 20 without the additional incorporation of bile salts.

Example 6 Testing different solvent S/Tween 20 ratios

Different stock solutions of substrate are prepared in DMSO in the presence of Tween® 20. Each stock solution corresponds to a different DMSO/Tween® 20 ratio. A volume corresponding to a final concentration of 500 mg/l of substrate is then added to a supercooled gelled medium, namely MacConkey medium. Table 7 below shows the composition of the six media tested. TABLE 7 Medium 1 2 3 4 5 6 % of DMSO in the 10% 20% 30% 40% 50% 60% stock solution % of Tween ® 20 added 90% 80% 70% 60% 50% 40% to the stock solution of substrate

Microorganisms originating from the Applicant's collection were inoculated onto each of the six media described above from a 0.5 McFarland suspension by isolation in three quadrants. The dishes were incubated at 37° C. for 48 hours. The colonies formed were examined visually after 24 and 48 hours of incubation. The coloration of these colonies and the intensity of this coloration were noted. The results are shown in Table 8 below. TABLE 8 Medium 1 2 3 4 5 6 Strain IT C I C I C I C I C I C I Salmonella 24 gray 2.5 gray 2.5 gray 2 gray 3 gray 3 gray 3 typhimurium 10 48 gray 3 gray 3 gray 2.5 gray 3.5 gray 3 gray 3.5 Salmonella 24 gray 2.5 gray 2.5 gray 3 gray 3.5 gray 3 gray 3.5 arizonae 15 48 gray 2.5 gray 2.5 gray 3 gray 3.5 gray 3 gray 3.5 Serratia 24 gray 3 gray 3 gray 3 gray 4 gray 3.5 gray 3.5 marcescens 045 48 gray 4 gray 4 gray 4 gray 4 gray 4 gray 4 Hafnia alvei 24 — — — — — — — — — — — — 025 48 — — — — — — — — — — — — Pseudomonas 24 gray 2 gray 2 gray 3 gray 3 gray 3 gray 3 aeruginosa 165 48 gray 2 gray 2 gray 2 gray 3 gray 3 gray 3 Salmonella 24 gray 1.5 gray 1.5 gray 2 gray 3 gray 2.5 gray 3 paratyphi A 006 48 gray 2 gray 2 gray 2 gray 3 gray 3 gray 3 Salmonella 24 gray 2 gray 2 gray 2 gray 3 gray 2 gray 3 typhi 118 48 gray 2 gray 2 gray 2 gray 3 gray 2 gray 3 I: intensity of coloration (arbitrary scale); C: color; IT: incubation time in hours; —: colorless

The six ratios tested make it possible to obtain a good substrate solubility and to reveal hydrolysis of the substrate with very acceptable intensities of coloration. Maximum intensities of coloration are obtained between the ratios 40% DMSO/60% Tween® 20 and 60% DMSO/40% Tween® 20.

Example 7 Testing the Method of Solubilization on an Esterase Substrate Having a Marker Other than an Indoxyl

The substrate tested is 1,2-dihydroxyanthraquinone octanoate (2-alizarin octanoate). Different stock solutions of substrate are prepared with DMF, DMSO, methanol or methoxyethanol as solvent and in the presence of Tween® 20 in all cases. Table 9 below shows the appearance of the stock solutions according to their composition. TABLE 9 Solvent of the stock solution methanol DMSO DMF methoxyethanol % of solvent in 40% the stock solution % of Tween ® 20 60% added to the stock solution of substrate Appearance of the precipitate precipitate total total stock solution dissolution dissolution

A volume corresponding to a final concentration of 100 mg/l of substrate is then added to a supercooled gelled medium, namely MacConkey medium. Iron citrate at a final concentration of 50 mg/l was also added to the medium so that the esterase activity could be revealed in the presence of an alizarin-based substrate. Only one of the stock solutions exhibiting total dissolution of the substrate was tested (stock solution in DMF). Microorganisms originating from the Applicant's collection were inoculated onto each of the two media described above from a 0.5 McFarland suspension by isolation in three quadrants. The dishes were incubated at 37° C. for 48 hours. The colonies formed were examined visually after 24 and 48 hours of incubation. The coloration of these colonies and the intensity of this coloration were noted. The results are shown in Table 10. TABLE 10 incubation medium with DMF Strain time color intensity Salmonella typhimurium 24 h mauve 1 10 48 h mauve 2 Salmonella enteritidis 24 h mauve 1 036 48 h mauve 3 Salmonella arizonae 24 h mauve 1 018 48 h mauve 2 Escherichia coli 24 h — — 002 48 h — — Serratia marcescens 24 h mauve 3.5 045 48 h mauve 3.5 Staphylococcus aureus 24 h mauve 3 033 48 h mauve 4 Pseudomonas aeruginosa 24 h mauve 2 165 48 h mauve 2 Salmonella gallinarum 24 h mauve 0.5 500 48 h mauve 3 intensity of coloration: arbitrary scale; —: absence of coloration or intensity

This mode of dissolution is therefore not specific for indoxyl esters, but can be used especially with other families of enzyme substrates.

Example 8 Testing different FASE derived from Tween® 20 for the solubilization of the esterase substrate 5-bromo-3-indolyl nonanoate

Different stock solutions of substrate are prepared in DMSO in the presence of Tween® 20, Tween® 80 (polyethoxylated sorbitan monooleate), Tween® 60 (polyethoxylated sorbitan monostearate) or Tween® 65 (polyethoxylated sorbitan tristearate). A volume corresponding to a final concentration of 500 mg/l of substrate is then added to a supercooled gelled medium, namely MacConkey medium. Table 11 shows the composition of the media tested. TABLE 11 Medium 1 2 3 4 % of DMSO in the stock solution 40% 40% 40% 40% % of Tween 20 added to the 60% — — — stock solution of substrate % of Tween 60 added to the — 60% — — stock solution of substrate % of Tween 65 added to the — — 60% — stock solution of substrate % of Tween 80 added to the — — — 60% stock solution of substrate

Microorganisms originating from the Applicant's collection were inoculated onto each of the six media described above from a 0.5 McFarland suspension by isolation in three quadrants. The dishes were incubated at 37° C. for 48 hours. The colonies formed were examined visually after 24 and 48 hours of incubation. The coloration of these colonies and the intensity of this coloration were noted. The results are shown in Table 12. TABLE 12 Medium 1 2 3 4 Strain IT C I C I C I C I Salmonella 24 h gray 2.5 gray 2 — — gray 2 typhimurium 10 48 h gray 3 gray 2 — — gray 2 Salmonella 24 h gray 2.5 gray 1 — — gray 1 arizonae 15 48 h gray 3 gray 2 — — gray 3 Salmonella 24 h gray 1.5 gray 1 — — gray 1 paratyphi A 006 48 h gray 3.5 gray 2 — — gray 3 Salmonella 24 h gray 2 gray 1 — — gray 1 typhi 118 48 h gray 2.5 gray 2 — — gray 2 Pseudomonas 24 h gray 3 gray 0.5 — — gray 4 aeruginosa 165 48 h gray 3 gray 2 — — gray 4 Hafnia alvei 24 h — — — — — — — — 025 48 h — — — — — — — — I: intensity of coloration (arbitrary scale); C: color; IT: incubation time; —: colorless

Note: Different Tween®/solvent ratios were prepared for each Tween® tested. However, only one ratio is listed in this Example because the results were very similar, irrespective of the ratio studied.

Tween® 20, Tween® 80 and Tween® 60 make it possible to obtain a good substrate solubility and to reveal hydrolysis of the substrate with very acceptable intensities of coloration.

Example 9 Comparative Stability of Gelled Media Containing the Esterase Substrate 5-bromo-3-indolyl Nonanoate Solubilized or Not Solubilized in the Presence of Tween® 20

Two stock solutions of substrate were prepared, one having a concentration of 40 g/l in methanol in the presence of 6.5 g/l of no. 3 bile salts, and the other having a concentration of 40 g/l in a mixture of DMSO (40%) and Tween® 20 (60%). A volume corresponding to a final concentration of 500 mg/l of substrate was then added to a supercooled gelled medium, namely MacConkey medium. These two media were poured into Petri dishes of diameter 90 mm and stored at +4° C. for 8 weeks. After one week, two weeks, four weeks and eight weeks, two media like those described above were prepared for immediate use.

Microorganisms originating from the Applicant's collection were inoculated from a 0.5 McFarland suspension, by isolation in three quadrants, onto the two media prepared for immediate use and the two media stored at +4° C. The dishes were incubated at 37° C. for 48 hours. The colonies formed were examined visually after 24 and 48 hours of incubation. The coloration of these colonies and the intensity of this coloration were noted. The results are shown in the Tables below. TABLE 13 stored for stored for fresh 1 week fresh 1 week methanol methanol DMSO DMSO Medium bile salts bile salts Tween 20 Tween 20 Strain IT C I C I C I C I Salmonella typhimurium 24 h gray 0.5 gray 0.5 gray 3 gray 3 10 48 h gray 1.5 gray 1.5 gray 4 gray 4 Salmonella arizonae 24 h gray 1 gray 1 gray 3 gray 3 15 48 h gray 1.5 gray 1.5 gray 4 gray 4 Salmonella paratyphi A 24 h — — — — gray 2 gray 2 006 48 h gray 0.5 gray 0.5 gray 4 gray 4 Salmonella typhi 24 h gray 0.5 gray 0.5 gray 3 gray 3 118 48 h gray 1.5 gray 1.5 gray 4 gray 4 Pseudomonas aeruginosa 24 h gray 1 gray 1 gray 2 gray 2 165 48 h gray 1 gray 1 gray 3 gray 3 Hafnia alvei 24 h — — — — — — — — 025 48 h — — — — — — — —

TABLE 14 stored for stored for fresh 2 weeks fresh 2 weeks methanol methanol DMSO DMSO Medium bile salts bile salts Tween 20 Tween 20 Strain IT C I C I C I C I Salmonella 24 h gray 0.5 gray 0.5 gray 3 gray 3 typhimurium 10 48 h gray 1.5 gray 1.5 gray 4 gray 4 Salmonella 24 h gray 1 gray 0.1 gray 3 gray 3 arizonae 15 48 h gray 1.5 gray 0.5 gray 4 gray 4 Salmonella A 24 h — — — — gray 2 gray 2 paratyphi 006 48 h gray 0.5 gray 0.1 gray 4 gray 4 Salmonella 24 h gray 0.5 — — gray 3 gray 3 typhi 118 48 h gray 1.5 gray 0.5 gray 4 gray 4 Pseudomonas 24 h gray 1 gray 1 gray 2 gray 2 aeruginosa 165 48 h gray 1 gray 1 gray 3 gray 3 Hafnia alvei 24 h — — — — — — — — 025 48 h — — — — — — — —

TABLE 15 stored for stored for fresh 4 weeks fresh 4 weeks methanol methanol DMSO DMSO Medium bile salts bile salts Tween 20 Tween 20 Strain IT C I C I C I C I Salmonella 24 h gray 0.5 — — gray 3 gray 3 typhimurium 10 48 h gray 1.5 gray 0.5 gray 4 gray 4 Salmonella 24 h gray 1 gray 0.1 gray 3 gray 3 arizonae 15 48 h gray 1.5 gray 0.5 gray 4 gray 4 Salmonella 4 24 h — — — — gray 2 gray 2 paratyphi A 006 48 h gray 0.5 gray 0.1 gray 4 gray 4 Salmonella 24 h gray 0.5 — — gray 3 gray 3 typhi 118 48 h gray 1.5 gray 0.5 gray 4 gray 4 Pseudomonas 24 h gray 1 gray 0.5 gray 2 gray 2 aeruginosa 165 48 h gray 1 gray 1 gray 3 gray 3 Hafnia alvei 24 h — — — — — — — — 025 48 h — — — — — — — —

TABLE 16 stored for stored for fresh 8 weeks fresh 8 weeks methanol methanol DMSO DMSO Medium bile salts bile salts Tween 20 Tween 20 Strain IT C I C I C I C I Salmonella 24 h gray 0.5 — — gray 3 gray 2.5 typhimurium 10 48 h gray 1.5 gray 0.5 gray 4 gray 3.5 Salmonella 24 h gray 1 — — gray 3 gray 3 arizonae 15 48 h gray 1.5 gray 0.5 gray 4 gray 3 Salmonella 24 h — — — — gray 2 gray 1.5 paratyphi A 006 48 h gray 0.5 — — gray 4 gray 3 Salmonella 24 h gray 0.5 — — gray 3 gray 2 typhi 118 48 h gray 1.5 gray 0.5 gray 4 gray 3 Pseudomonas 24 h gray 1 gray 0.5 gray 2 gray 2 aeruginosa 165 48 h gray 1 gray 1 gray 3 gray 3 Hafnia alvei 24 h — — — — — — — — 025 48 h — — — — — — — — I: intensity of coloration (arbitrary scale); C: color; IT: incubation time; —: colorless

The medium containing the substrate dissolved in a mixture of methanol and bile salts exhibits a very substantial drop in the expression of esterase activity after storage for 2 weeks. This drop is amplified over time. The medium containing the substrate dissolved in a mixture of DMSO and Tween 20 exhibits a constant expression of esterase activity over time up to at least six weeks. After eight weeks there is a slight but not prohibitive drop in the expression of esterase activity. Tween 20 therefore makes it possible to stabilize the esterase substrate and makes it easier to store and use culture media containing this type of substrate.

Note: In the above Examples, the numbers following the strains correspond to the number of each strain referenced in the Applicant's collection. The intensity of coloration corresponds to an arbitrary scale defined as follows: 0 no activity 0.1 trace of coloration 0.5 very pale coloration 1 distinct coloration of low intensity 2 clear coloration of medium intensity 3 intense coloration 4 very intense coloration

Example 10 Comparative Stability of Gelled Media Containing the Osidase Substrate 6-chloro-3-indolyl-β-N-acetylglucosaminide Solubilized or Not Solubilized in the Presence of Tween® 20

Two stock solutions of substrate were prepared, one having a concentration of 50 g/l in DMF and the other having a concentration of 50 g/l in a mixture of DMF (40%) and Tween® 20 (60%). A volume corresponding to a final concentration of 175 mg/l of substrate was then added to a supercooled gelled medium, namely Columbia medium not supplemented with blood. These two media were poured into Petri dishes of diameter 90 mm and stored at +4° C. for 8 weeks. After three weeks, six weeks, nine weeks and twelve weeks, two media like those described above were prepared for immediate use.

Microorganisms originating from the Applicant's collection were inoculated from a 0.5 McFarland suspension, by isolation in three quadrants, onto the two media prepared for immediate use and the two media stored at +4° C. The dishes were incubated at 37° C. for 48 hours. The colonies formed were examined visually after 24 and 48 hours of incubation. The coloration of these colonies and the intensity of this coloration were noted. The results are shown in the Tables below. TABLE 17 stored for stored for fresh 3 weeks fresh 3 weeks DMF DMF Medium DMF DMF Tween 20 Tween 20 Strain IT C I C I C I C I Listeria 24 h M 2 M 1.5 M 2 M 2 innocua 36 48 h M 3 M 3 M 3 M 3 Listeria 24 h M 1.5 M 1 M 1.5 M 1.5 ivanovii 18 48 h M 2.5 M 2.5 M 2.5 M 2.5 Listeria 24 h M 2 M 1.5 M 2 M 2 monocytogenes 23 48 h M 3 M 3 M 3 M 3 Staphylococcus 24 h — — — — — — — — aureus 20 48 h — — — — — — — — Pseudomonas 24 h — — — — — — — — aeruginosa 165 48 h — — — — — — — —

TABLE 18 stored for stored for fresh 6 weeks fresh 6 weeks DMF DMF Medium DMF DMF Tween 20 Tween 20 Strain IT C I C I C I C I Listeria 24 h M 2 M 1 M 2 M 2 innocua 36 48 h M 3 M 2 M 3 M 3 Listeria 24 h M 1.5 M 0.5 M 1.5 M 1.5 ivanovii 18 48 h M 2.5 M 2 M 2.5 M 2.5 Listeria 24 h M 2 M 1 M 2 M 2 monocytogenes 23 48 h M 3 M 2 M 3 M 3 Staphylococcus 24 h — — — — — — — — aureus 20 48 h — — — — — — — — Pseudomonas 24 h — — — — — — — — aeruginosa 165 48 h — — — — — — — —

TABLE 19 stored for stored for fresh 9 weeks fresh 9 weeks DMF DMF Medium DMF DMF Tween 20 Tween 20 Strain IT C I C I C I C I Listeria 24 h M 2 M 0.5 M 2 M 1.5 innocua 36 48 h M 3 M 1 M 3 M 2.5 Listeria 24 h M 1.5 M — M 1.5 M 1 ivanovii 18 48 h M 2.5 M 0.5 M 2.5 M 2.5 Listeria 24 h M 2 M 0.5 M 2 M 1 monocytogenes 23 48 h M 3 M 0.5 M 3 M 2 Staphylococcus 24 h — — — — — — — — aureus 20 48 h — — — — — — — — Pseudomonas 24 h — — — — — — — — aeruginosa 165 48 h — — — — — — — —

TABLE 20 stored for stored for fresh 12 weeks fresh 12 weeks DMF DMF Medium DMF DMF Tween 20 Tween 20 Strain IT C I C I C I C I Listeria 24 h M 2 M — M 2 M 1 innocua 36 48 h M 3 M 0.5 M 3 M 2.5 Listeria 24 h M 1.5 M — M 1.5 M 1 ivanovii 18 48 h M 2.5 M — M 2.5 M 2 Listeria 24 h M 2 M — M 2 M 1 monocytogenes 23 48 h M 3 M — M 3 M 2 Staphylococcus 24 h — — — — — — — — aureus 20 48 h — — — — — — — — Pseudomonas 24 h — — — — — — — — aeruginosa 165 48 h — — — — — — — — I: intensity of coloration (arbitrary scale); C: color; IT: incubation time; M: magenta; —: colorless

The medium containing the substrate dissolved in DMF alone exhibits a very substantial drop in the expression of β-N-acetylglucosaminidase activity after storage for three weeks. This drop is amplified over time. Activity can no longer be detected after twelve weeks. The medium containing the substrate dissolved in a mixture of DMF and Tween 20 exhibits a constant expression of β-N-acetylglucosaminidase acivity over time up to at least six weeks. After nine and twelve weeks, there is a slight but not prohibitive drop in the expression of β-N-acetylglucosaminidase activity. Tween 20 therefore makes it possible to stabilize the β-N-acetylglucosaminidase substrate and makes it easier to store and use culture media containing this type of substrate.

In the above Examples, the numbers following the strains correspond to the number of each strain referenced in the Applicant's collection. The intensity of coloration corresponds to an arbitrary scale defined as follows: 0 no activity 0.1 trace of coloration 0.5 very pale coloration 1 distinct coloration of low intensity 2 clear coloration of medium intensity 3 intense coloration 4 very intense coloration 

1-15. (cancelled)
 16. Medium for the detection/identification of micro-organisms, especially bacteria and/or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities that is of the type comprising especially a reaction medium and at least one chromogenic or fluorogenic esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrate, with the exclusion of substrates comprising a 4-[2-(4-octanoyloxy-3,5-dimethoxyphenyl)vinyl]quinolinium-1-(propan-3-ylcarboxylic acid) cation and an anion, this detection/identification being based essentially on revealing the presence of the esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activity, wherein the improvement consists essentially in that said medium: is in a stable, ready-to-use liquid or gel form; and contains: at least one fatty acid sorbitan ester (FASE) or at least one fatty acid (FA) or an FASE/FA mixture as an emulsifying stabilizer, and optionally at least one solvent (S).
 17. Medium according to claim 16, obtained by mixing at least one stock solution of substrate in the solvent S, with FASE, FA or an FASE/FA mixture, and with at least some of the constituents of the culture medium.
 18. Medium according to claim 16, wherein the FASE is selected from the group comprising: polyethoxylated sorbitan monolaurate containing 20 units of ethylene oxide (EO); polyethoxylated sorbitan monopalmitate (20 EO); polyethoxylated sorbitan monostearate (20 EO); polyethoxylated sorbitan tristearate (20 EO); polyethoxylated sorbitan monooleate (20 EO); polyethoxylated sorbitan sesquioleate (20 EO); polyethoxylated sorbitan trioleate (20 EO); and mixtures thereof.
 19. Medium according to claim 16, wherein the FA is selected from the group comprising C4-C20 saturated or unsaturated fatty acids, preferably C6-C11 saturated or unsaturated fatty acids and particularly preferably C8-C9 fatty acids, and mixtures thereof.
 20. Medium according to claim 16, also comprising at least one anionic surfactant, preferably 7-ethyl-2-methyl-4-undecyl hydrogensulfate or its salts, more particularly its sodium salts.
 21. Medium according to claim 16, wherein the chromogenic or fluorogenic substrate consists of a target part for the enzyme and a chromophoric or fluorophoric part, the target part being selected from the group comprising the following in particular: glycosides consisting of mono-, di- and/or polysaccharide units linked in the α- or β-position to the hydroxyl group of the fluorophoric or chromophoric part; α-amino acids or peptides; organic acids such as —O—CO(CH₂)_(n)—CH₃, where n is between 0 and 20; and a sulfate, a phosphate, a pyrosulfate, a pyrophosphate and a phosphodiester, and the chromophoric or fluorophoric part being selected from the group comprising the following in particular: quinones/anthraquinones and derivatives, especially dihydroxyanthraquinone (alizarin); amino- and hydroxycoumarins and derivatives; fluoresceins and derivatives; and indoxyls and derivatives.
 22. Medium according to claim 16, wherein the solvent S is selected from the group comprising: alcohols, preferably methanol, ethanol and methoxyethanol; amides, preferably dimethylformamide; sulfur-containing solvents, preferably dimethyl sulfoxide; aqueous solvents, preferably water and buffered water; and mixtures thereof.
 23. Medium according to claim 16, wherein the proportion by weight of fatty acid sorbitan ester(s) (FASE) to solvent (S) is between 20:80 and 80:20, preferably between 30:70 and 70:30 and particularly preferably 40:60 or 60:40.
 24. Medium according to claim 16, wherein the concentration of (FASE) in the medium is defined as follows (in % by weight): 0.1 ≦ [FASE] ≦ 10, preferably 0.5 ≦ [FASE] ≦ 5, and particularly preferably 1.5 ≦ [FASE] ≦ 3.5.


25. Medium according to claim 16, wherein in that the concentration of substrate in the medium is defined as follows (in mg/l):  1 ≦ [substrate] ≦ 2000, preferably  5 ≦ [substrate] ≦ 1500, and particularly preferably 25 ≦ [substrate] ≦
 1000.


26. Medium according to claim 16, wherein the culture medium it contains is selected from the group comprising: selective media of the type comprising MacConkey, Columbia ANC, PALCAM and Sabouraud gentamycin-chloramphenicol media, preferably MacConkey medium; and non-selective media of the type comprising Columbia ±blood, trypcase soya, nutrient gelose and Sabouraud media, preferably Columbia medium.
 27. Medium according to claim 16, wherein in that the microorganisms to be detected/identified are microorganisms of medical or industrial interest, especially those of the genus Salmonella, Pseudomonas, Listeria, Staphylococcus, Enterococcus or Candida.
 28. Method of obtaining the medium according to claim 16, consisting essentially in: preparing at least one stock solution of the chromogenic or fluorogenic esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrate in the solvent S and of at least one FASE, FA or FASE/FA mixture, adding this solution and any other additives to the culture medium, and homogenizing the whole.
 29. Method for the detection/identification of strains with esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activity, consisting in: inoculating the medium according to claim 16, with the bacteria to be analyzed; incubating the inoculated medium under appropriate conditions; and reading and interpreting the colorations around the colonies, these colorations revealing hydrolysis of the substrate by the bacteria.
 30. Method for the detection/identification of microorganisms, especially bacteria or yeasts, with an enzymatic activity selected from esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase activities, this medium comprising especially a culture medium and at least one chromogenic or fluorogenic esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrate, with the exclusion of substrates comprising a 4-[2-(4-octanoyloxy-3,5-dimethoxyphenyl)vinyl]quinolinium-1-(propan-3-yl)carboxylate and an anion, optionally in association with at least one solvent S for the chromogenic or fluorogenic esterase and/or osidase and/or peptidase and/or sulfatase and/or phosphatase substrate present in the medium: said method consisting essentially in using fatty acid sorbitan ester(s) (FASE), fatty acid(s) (FA) or FASE/FA as an emulsifying stabilizer for a medium (liquid or gel). 